Vehicle misfires under load, engine reved up to 2500-3000

ISLANDTECH_925

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1995 GMC SUBURBAN

V8

4WD

AUTOMATIC

250,000 MILES

95 GMC K2500 4X4 7.4L TBI.
I AM BACKFIRING UNDER LOAD, WHEN ITS COLD IT RUNS ROUGH THEN IT SMOOTHS OUT. IDLES AT 900-1000 RPMS. IT ALSO MISFIRES WHEN ITS COLD AND TRANSMISSION IS IN DRIVE? INTAKE MANIFOLD GASKET WAS REPLACED, TUNE UP DONE, PICK UP COIL REPLACED, COMPRESSION NORMAL @ 150 PSI.